The invention relates to an electron gun for a cathode ray tube, comprising:
insulator rods in the longitudinal direction l of the row, aside from the row of grids, which insulator rods maintain the grids positioned with respect to each other;
metal brackets having a base and juxtaposed legs on sides of the base, said legs of each bracket being welded to the lateral wall of a respective bush-shaped grid and being embedded in a respective insulator rod by means of their lugs, which lugs face away from the legs.
The invention also relates to a cathode ray tube provided with such an electron gun.
An electron gun of this type is known from EP-A-0 453 978.
It is important for the sharpness of the image, which is produced by means of the gun in a cathode ray tube, that the grids of the gun are mutually aligned within narrow tolerances. To this end, the grids of the gun are mechanically secured to each other by means of insulator rods of, for example, glass, while they are maintained aligned with respect to each other by means of, for example, a jig. After mechanical assembly of the gun, electric conductors are secured to the grids, which conductors are connected to contact pins embedded in an insulating, for example glass, flange. At a later stage, a fuse is made at this flange with the neck of a cathode ray tube.
The known electron gun is manufactured by first embedding the metal brackets in the insulator rods, by subsequently welding the brackets to the bush-shaped grids while maintaining them aligned with respect to each other and by subsequently welding the electric conductors to the grids.
The brackets of the known electron gun have their legs on the shorter sides of the base. The legs are outwardly flanged and welded joints with the grids are realized on the flanged portions, aside from the insulator rods. The base extends transversely to the insulator rods and is entirely shielded by an insulator rod. The lugs embedded in an insulator rod are bent from the plane of the base on its longer sides and face away from the legs.
Another electron gun known from the quoted document has U-shaped brackets. The base of these brackets completely engages the grids and is welded thereto. The legs themselves are embedded in the insulator rods. The brackets have no lugs.
Yet another electron gun known from this document also has U-shaped brackets whose legs are outwardly flanged. The base of the brackets is completely embedded in the insulator rods. Welded joints with the grids are realized on the flanged portions of the legs which project laterally from the insulator rods. Also these brackets have no lugs.
With the construction of the known electron gun described in the opening paragraph, it is envisaged, likewise as with the two other known electron guns, to prevent differences in size and mutual position of the grids in electron guns from one batch. Such differences affect the properties of the electron gun, notably the sharpness of the image given by a cathode ray tube provided with the electron gun.
It is a drawback of the known electron guns there is still a relatively large spread of the properties of the guns from one batch. This spread might lead to deformation of the grids during assembly of the electron guns when a first bracket embedded in an insulator rod already makes contact with a first grid while the insulator rod must still be further moved towards the grids so as to bring the other brackets into contact with the other grids.
It is an object of the invention to provide an electron gun of the type described in the opening paragraph in which the risk of spread of properties of guns from one batch is obviated.
According to the invention, this object is achieved in that the base of the brackets extends as far as the side of the relevant insulator rod, and in that electric conductors are welded to the base, which electric conductors are connected to contact pins embedded in an insulating flange.
The invention is based on the recognition that deformations of the grids and hence disturbance of their aligned position may be the result when the conductors are welded to the grids themselves, as is the case in the known electron gun. In the electron gun according to the invention, this is obviated in that the conductors are welded to the base of the brackets. The brackets stiffen the grids and, during welding, constitute a mechanical and thermal buffer for the grids themselves. Moreover, the electron gun may be made in a conventional manner by welding the brackets to the grids prior to the alignment step. The local thermal and mechanical load of the grids resulting from the welding operation then occurs prior to the alignment. Another advantage is that the grids are then still accessible internally and externally so that not only laser welding but also, for example, resistance welding is still possible.
Individual guns of a batch of electron guns according to the invention have mutually different properties to a small extent only and are substantially equal for practical applications.
The legs of the brackets may extend in the longitudinal direction l of the row, for example, parallel to the insulator rods. However, it is favorable when the legs are transverse to the longitudinal direction l of the row. The legs then have a relatively large width and a relatively long contact with the grid. Welds can then be made on the grid at locations which are spaced far apart on each of the two legs so that the grid is mechanically strengthened to a large extent.
To this end, it is favorable when the base has longer sides and the legs have a width which essentially corresponds to the longer sides of the base. Then they have a relatively long contact line with the grids.
The lugs of the brackets may be situated in areas transverse to the legs, for example, along sides of the base and connected thereto. However, it is favorable when the lugs are cut loose from the base and are bent outwards, for example, transverse to the longer sides of the base and leaving an opening in the base. This embodiment limits the quantity of material for the brackets.
In a variant of this embodiment, the lugs extend in alignment with the legs. This variant has the advantage that the lugs are spaced far apart, just as far as the legs, and the brackets yield a very stable coupling with the insulator rods. An important advantage is, however, the simplicity of manufacture of the brackets. When an in-plano of the brackets is obtained by means of, for example, punching from, for example, sheet material, bending in only one direction needs to take place only twice for realizing this variant so as to bend the legs, and simultaneously the lugs, from the plane of the base. Moreover, the two bending operations may be easily performed simultaneously in one operating step. This variant is superior to the bracket of the known electron gun, both as far as material quantity and simplicity of manufacture and function are concerned.
It is favorable when the brackets extend on both sides as far as the sides of the insulator rod. It is then possible to connect the electric conductors on the one or the other side of the one or the other insulator rod to the brackets and hence space each conductor relatively far apart from the other.
It is favorable when each leg of the brackets is entirely located in a flat plane so that they do not have any flanged end portions. In this embodiment, the brackets can only be secured to the grids by means of butt-welding. In contrast to welding on flanged portions of the legs, the brackets then give the grids great stiffness and stability. Furthermore, the material quantity required for the brackets is smaller and their manufacture is simpler.
It is favorable when the insulator rods consist of glass.
The electron gun according to the invention may be designed for generating only one electron beam in a monochrome cathode ray tube, or for generating three electron beams in a multichrome cathode ray tube. In such a cathode ray tube, a multitude of colors is generated by means of phosphors in three colors, for example, red, green and blue.
The cathode ray tube according to the invention may be a monochrome tube or a multichrome tube. The tube may be intended for use as a computer monitor, in a television receiver, or in an oscilloscope.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.